Effective water purification is critical for our mining operations. Only purified water complying with threshold values set by the authorities is led from the mine to the nearby watercourse areas or Lake Nuasjärvi.
The water used in the production and the annual precipitation in the mine's production area are purified effectively with lime. Wastewater treatment based on lime neutralisation is a very commonly used purification method at mines both in Finland and globally. Lime neutralisation is generally considered a purification method compatible with the best available techniques (BAT).
The first phase of the production water purification is preneutralisation, which is performed at the metals production plant. From there, the purified water is diverted to the reverse osmosis plant (RO) where production water is produced and recycled for the metals production plant's most demanding applications. Thus, water intake from outside the production process is significantly reduced. The sulphate-containing reject is returned to the bioleaching heaps, which provides significant benefits to Terrafame’s sulphate balance management.
In addition, each year about 6 million cubic meters of water rains or melts at Terrafame's production areas, even though the catchment area has been significantly restricted by building separation trenches and dams. Due to the metal-containing soil and production operations, the water becomes dirty and the precipitation water in the production area has to be purified before the water is diverted away from the area. Lime purification is a reliable and uniform method for precipitation waters and drainage waters of the open pit mine during all seasons.